running the engine at full throttle when it's running very rich is okay cos the RPMs won't build up due to the rich setting.
the engine will make '4-stroke engine' kind of sound.
if you go to RB's website, rody has recommended a similar way of breaking in engines.

as for the P5X's carb, it's still the old design. you gotta turn the carb around to do the linkage. when i got my P5TX, i was also surprised it didn't come with the new carb design...
the newer nova plus21-5 has the proper design which is meant for buggies...
then again, not really a big deal cos the main prob wif the old design was tt reaching the idle screw was abit diff, that's all...